[turbofan] Assign appropriate types to RegExp builtins.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index 99c8fa887267fdf0358191a23aa197158d81aad6..00eafe0d4809896e6cbff200a33cf841d63a7558 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -1415,6 +1415,16 @@ Type* Typer::Visitor::JSCallFunctionTyper(Type* fun, Typer* t) {
         case kObjectHasOwnProperty:
           return Type::Boolean();
 
+        // RegExp functions.
+        case kRegExpCompile:
+          return Type::OtherObject();
+        case kRegExpExec:
+          return Type::Union(Type::OtherObject(), Type::Null(), t->zone());
+        case kRegExpTest:
+          return Type::Boolean();
+        case kRegExpToString:
+          return Type::String();
+
         // Function functions.
         case kFunctionHasInstance:
           return Type::Boolean();